lab9/act2/WoolieQueue.java

   1 /*
   2  * WoolieQueue.java
   3  * $Id: WoolieQueue.java,v 2.4 2005/01/26 04:15:44 vcss232 Exp $
   4  *
   5  * Revisions:
   6  *      $Log: WoolieQueue.java,v $
   7  *      Revision 2.4  2005/01/26 04:15:44  vcss232
   8  *      Added generics (jeh)
   9  *
  10  *      Revision 2.3  2004/04/12 23:49:05  cs3
  11  *      moved the instance variables to the top of the class (bk)
  12  *
  13  *      Revision 2.2  2004/01/21 20:05:08  icss235
  14  *      Reversed order from LIFO to FIFO (jeh)
  15  *
  16  *      Revision 2.1  2004/01/21 16:43:43  icss235
  17  *      Simplified design. (jeh,swm)
  18  *
  19  *      Revision 2.0  2004/01/20 22:06:59  icss235
  20  *      *** empty log message ***
  21  *
  22  */
  23
  24 /**
  25  * A multithread-safe wrapper around a linked list to make a queue.
  26  *
  27  * @author James Heliotis
  28  */
  29 public class WoolieQueue {
  30
  31         /**
  32          * The underlying data structure
  33          */
  34         private java.util.LinkedList< Woolie > woolies =
  35                                  new java.util.LinkedList< Woolie >();
  36
  37
  38         /**
  39          * Constructor. Does nothing in this version.
  40          */
  41         public WoolieQueue() {
  42         }
  43
  44         /**
  45          * Insert a woolie into the queue.
  46          *
  47          * @param caller the Woolie to be inserted.
  48          */
  49         public synchronized void insert( Woolie caller ) {
  50                 woolies.addFirst( caller );
  51                 notifyAll();
  52         }
  53
  54         /**
  55          * Inspect the first woolie in the queue.
  56          * This method never blocks.
  57          *
  58          * @return the Woolie that has been in the queue for
  59          *         the longest time, or null if the queue is
  60          *         empty.
  61          */
  62         public synchronized Woolie peek() {
  63                 Woolie result = null;
  64                 try {
  65                         result = woolies.getLast();
  66                 }
  67                 catch( java.util.NoSuchElementException nse ) {
  68                 }
  69                 return result;
  70         }
  71
  72         /**
  73          * Remove a woolie from the queue.
  74          * This call blocks while the queue is empty.
  75          *
  76          * @return the Woolie that has been in the queue for
  77          *         the longest time.
  78          */
  79         public synchronized Woolie remove() {
  80                 while ( woolies.isEmpty() ) {
  81                         try {
  82                                 wait();
  83                         }
  84                         catch( InterruptedException ie ) {}
  85                 }
  86                 return woolies.removeLast();
  87         }
  88 }